Catalystic fines in fuel oil

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					                                           Service Bulletin                                                                  G–9
                                           Technical Information to all Owners / Operators
                                           of Sulzer Diesel Engines

                                           Catalyst Fines in
                                           Heavy Fuel Oils

                                                                                                      Contents:                          Pages

                                                                                                  1. Introduction                          1
                                                                                                  2. Identifying the Effect of             1
                                                                                                     Catalyst Fines
                                                                                                  3. Analysing for Catalyst Fines         2
                                                                                                     and Interpreting the Findings
                                                                                                  4. Action to take when                   3
                                                                                                     Catalyst Fines are present
                                                                                                  5. Fuel Oil Treatment Arrangement        4
                                                                                                  6. Size, Shape, Composition              5
                                                                                                     and Uses
                                                                                                  7. Conclusion                            6 – Printed in Switzerland

                                                                                                  8. G + S Service Bulletins Published    6
                                                                                                     for Sulzer Diesel Engines
                                                     Enlarged Cylinder Liner Surface
                                                     Replica with Catalyst Fines

                                       Wärtsilä NSD Switzerland Ltd   PO Box 414           Tel. +41 52 262 49 22
                                       Wärtsilä NSD Schweiz AG        CH-8401 Winterthur   Fax +41 52 212 49 17
                                       Wärtsilä NSD Suisse SA         Switzerland          Tlx 896 659 NSDL CH

 Catalyst fines (cat fines) are often found in heavy fuel oils. They are a common cause of high
 piston ring and cylinder liner wear in low speed diesel engines, but in Sulzer trunk piston
 engines the problems are less common. If fuel containing cat fines is bunkered, they must be
 removed before the fuel reaches the engine. Cat fines are found by an analysis of the
 aluminium (Al) and silicon (Si) content of the fuel oil. The Wärtsilä NSD fuel specification
 allows a maximum combined content of 80 mg/Kg aluminium and silicon as bunker limit. An
 aluminium and silicon content of up to 15 mg/kg is tolerable after treatment at engine inlet.


 The sudden emergence of excessive piston ring and cylinder liner wear in low speed diesel
 engines on all cylinders is often caused by cat fines in the fuel oil. The presence of cat fines can
 be recognised by erosion on the spill valve stem of the fuel pump and by the numerous particles
 found embedded in the graphite flakes of the running surfaces on microscopic examination of
 rings and liner replicas (see Fig. 1 and Fig. 2). Cat fines primarily cause three body abrasion of
 ring and liner, but some are retained in the graphite flakes of the metal surface and these
 continue to abrade the running partners for a long time after they have entered the engine.
 When the running surface of an older liner is examined microscopically it is often possible to
 find a few cat fines trapped in the surface structure and worn down level with the surface. Cat
 fines are hard abrasive particles, 5 to 50 microns in size. The particles of 10 to 20 microns are the
 most dangerous, as they are most readily caught in the oil film and in the fine graphite structure
 of rings and liners. Smaller particles tend not to cause wear and larger particles are not easily
 held in the oil film.

          Piston Ring Surface                                  Same Piston Ring Surface
          Magnification: 280:1                                 Magnification: 1'200:1
Comment: Severe abrasion on running                  Comment: Catalytic fines approx. 10 microns
surface, cat fines trapped in graphite flake.        in diameter with a hardness of 824 Vickers.
                     Fig. 1      Microscopic Examination of Replicas

                                                1/8                          Service Bulletin G-9
                                                          Cylinder Liner Surface
                                                          TDC, Exhaust side
                                                          Magnification of replica: 84:1

                                                          A lot of cat fines embedded in the
                                                          matrix. Strong abrasive wear due to
                                                          cat fines.

                                                          Cat Fines

 Fig. 2        Microscopic Examination of Replicas

The main problem caused by cat fines is ring and liner wear. But if the fuel oil is heavily
contaminated with cat fines then there can be problems on all exposed surfaces:
       Fuel pumps:                             Seizure, wear (if particles size equals clearance
                                               between barrel and plunger)
       Fuel injection valves:                  Seizure, wear, on nozzle holes and needle seat
       Piston rod, piston rod stuffing boxes: Excessive wear, excessive supply of oil to piston rod
                                              stuffing box
A cylinder liner surface which has been roughened by cat fines is more susceptible to corrosive
wear, and the combination of cat fines and corrosive wear can be very severe. The wear profile
of a cylinder liner damaged by cat fines shows high wear and sometimes a wear maximum in the
upper mid stroke region.


3.1.     Standard Test Methods
The presence of cat fines in fuel is determined by burning the fuel and roasting the ash at 550°C.
The ash is then dissolved in very strong acid and the solution analysed for the two elements
aluminium and silicon, which are constituents of cat fines (ISO 10478:1994). Other less
common tests include measuring the quantity of centrifuge sediment and microscopic
examination of the sediment.

                                                2/8                        Service Bulletin G-9
3.2.     Why Catalyst Fines are not always found
Cat fines that are present in the fuel are sometimes not detected because of the problems of
taking and analysing representative samples:
       • The fuel oil sample is not always representative of the complete fuel oil bunker. Cat fines
         are not uniformly distributed in the fuel. They can settle out or be resuspended.
       • Aluminium and silicon content should not be measured directly, without firstly ashing the
         fuel oil, then roasting and dissolving the ash.
       • In the laboratory a one litre fuel oil sample is heated to 50 to 60°C and stirred for
         5 minutes before a smaller sample is removed for analysis. If this preparation is neglected
         or insufficient, cat fines which have settled to the bottom are not found in the smaller

3.3.     Field Observations
In one case a large reduction in cat fines was observed during fuel storage, most likely because
the cat fines had settled out. Another time cat fines were found after storage where before there
had been none. Cat fines, at levels that are not apparent in the fuel analysis, can accumulate in
the tanks from successive deliveries. During heavy weather they will be churned up. It is usually
not possible to take samples from the bottom of the tank.
In another case a small but definite increase in liner wear was observed, when the content of cat
fines in the fuel increased but stayed within the specification.
On more than one occasion when an engine was found to have suffered extreme wear due to cat
fines in the fuel oil, filter blocking or an increase in automatic filter back flushing had been
recorded. The filter usually had a mesh size which was larger than the average size of the cat fine

3.4.     The Density Method
A statistic of density plotted against aluminium plus silicon content showed that the combined
aluminium and silicon content only exceeds 10 mg/Kg when the fuel density is greater than
0.96 g/ml. High density does not indicate cat fines, but it seems that the risk of finding them is
greater. Heavy fuel oil is a mixture of various products of petroleum refining and the
components which contain cat fines tend to have a higher density.


4.1.     General
Cat fines are more common in some areas of the world than in others. If a vessel generally
receives fuel free from cat fines, less monitoring is required. But if cat fines are likely to be
present, then it is important to analyse the fuel oil more often, even more than once per bunker,
and to regularly clean out storage and settling tanks.
The bunker supplier should be informed when cat fines are found in the fuel which they supply.
We do not recommend exceeding the normal cylinder lube oil feed rate much, as a measure to
counteract cat fines. A certain flushing effect is possible, but it is probably not very effective and
other problems can occur if the lube oil feed rate is too high. An increase of approximately 20%
is tolerable.

                                                 3/8                         Service Bulletin G-9
After the engine has been damaged by cat fines in the fuel oil, piston rings with cat fines
embedded in them must be replaced and liners should be honed to remove the cat fines and
hard brittle layers caused by excessive wear. Otherwise damage will continue even if the fuel no
longer contains cat fines. Using a microscope it is possible to examine the rings and liners to
decide what action should be taken. Our Service Engineers are able to assist in such an

4.2.   Water
Cat fines are highly hydrophilic and if water is present they are incorporated into water
droplets. When the water is separated the cat fines are also removed. The density of fresh water
is similar to that of high density fuel at the separation temperature. If water, in particular fresh
water, cannot be removed in the fuel oil separator then the cat fines will also not be removed.
When the fuel oil is stirred, water is mixed in. It forms an emulsion and becomes more difficult
to separate. A decanter upstream from the separator hinders cat fine removal because of the
stirring effect. For the same reason the centrifuge should be as close as possible to the settling
The presence in the fuel oil of used automotive lubricating oil containing strong detergents is
thought to cause water to emulsify, making cat fine removal more difficult. Treating fuel
containing emulsified water with a demulsifying fuel additive can improve cat fine removal. The
separation efficiency of water is improved when water is removed from the fuel by evaporation
or distillation. This is not beneficial for the removal of cat fines. The water in the fuel is needed
in the separator to assist the removal of cat fines.


For the fuel oil tanks and treatment arrangements as well as fuel oil system, please refer to Fig. 3
and 4 respectively. For further information on fuel treatment please also refer to our Service
Bulletin Diesel Engine Fuels".

5.1.   Arrangement of Separators
For the correct arrangement of separators refer to the manufacturer's instruction. A separation
efficiency of minimum 80% should be achieved, i.e. 80% by weight of the impurities removed. If
separators with gravity discs are used, two separators must operate in parallel with
approximately 15% of the nominal volume flow rate. The best efficiency would be achieved
with two parallel purifiers feeding one clarifier (89%). Most of the separation is achieved in the
purifiers (70 to 80%), the clarifier giving the final polish".

5.2.   Separation Efficiency
Cat fines are removed by centrifuging the fuel oil. The separator is not equally efficient for all
sizes of cat fine particles; one theoretical calculation gave an efficiency minimum at a diameter
of 9 microns. The smallest particle that is removed in the centrifuge is a function of density
difference, viscosity (temperature dependant) and flow rate. This is theoretically and also for
cat fines experimentally approximately 5 microns, which means that the smallest particles are
neither removed by a centrifuge nor by a 5 micron filter.
The cat fines of diameter less than 10 microns are the most difficult to remove. The fuel
reaching the engine should not contain more than 15 mg/Kg aluminium plus silicon. The cat
fines remaining in the fuel after fuel treatment should consist mainly of these smaller particles.
All cat fines of diameter greater than 10 microns must be removed in the separator.

                                                4/8                         Service Bulletin G-9
The effective removal of cat fines is often lower than the calculated theoretical efficiency. The
theoretical calculation assumes solid spherical particles and uses an estimated density. The
most dangerous cat fines resemble fractured hollow balls. The effective density depends on
whether the pores are filled with water or fuel and therefore the estimated density is not always

5.3.   Filters
Cat fines are removed from the fuel oil in the separator and not in the filter. The Wärtsilä NSD
standard fuel oil filter of size maximum 50 microns is not intended to protect the engine against
cat fines. When the separator is functioning correctly no further protection is required.
Secondary back flush filter(s) (item 15 in Fig. 3 and 4) with a 10 micron mesh is / are used to
protect the engine from serious damage if for some reason the separator has not removed all the
cat fines from the fuel. In addition such a filter is a good indication of the separator efficiency. If
there is reason to suspect that the fuel oil contains cat fines, the backflush from the filter should
be transferred to the sludge tank and disposed of.
The most reliable way to avoid problems with cat fines completely is to use a 5 micron fine filter
at the engine inlet (a tertiary filter). However we do not recommend using a filter this fine
because they are easily blocked e.g. by asphaltene particles, particularly if the fuel stability is
low. Some engine owners use fuel homogenisers in combination with a 5 micron fine filter to
prevent the filter from blocking.


6.1.   Use of Catalyst in Oil Refining
Catalytic cracking is used by the majority of refineries. The high density cat bottoms or catalytic
cracking fractionator bottoms are blended to residual components to reduce the viscosity. The
high aromaticity of the bottoms increases the ability of heavy fuel fuel oil to dissolve asphaltenes
and thus reduces the risk of incompatibility.
If the fluidized catalytic cracking (FCC) operates correctly then the catalyst is recovered. The
catalyst is expensive and is not intended to be a waste product.
In recent years catalysts have been further developed. There is a trend towards harder catalysts,
which is good for the refinery, but not good for the diesel engine.

6.2.   Size and Shape
The catalyst in oil refining is very hard porous round particles. The catalysis takes place on the
surface of the particle. The particles must have the largest possible surface area to volume ratio,
be light enough to be easily transported and have a high crush strength.
The mean particle size of fresh catalyst is 70 microns (range 20 to 150 microns) and 75% of the
particles are larger than 25 microns. But the size is reduced during circulation in the refinery
and by the time the catalyst particle reaches the fuel oil as cat fines the average size has dropped
to less than 20 microns (range 3 to 42 microns). The largest particle size in fuel oil depends on
the settling history of the fuel.

                                                5/8                           Service Bulletin G-9
6.3.     Composition
In the past catalyst was made from pure silica (SiO2) or alumina (Al2O3). Now materials such as
faujosite, which is broadly similar to porcelain, are used. These materials contain not only
aluminium and silicon, but also smaller amounts of sodium, calcium, magnesium, potassium,
etc. The content of cat fines in heavy fuel oil by weight is 3 to 15 times that of aluminium. A good
approximation is that the amount of catalyst by weight is twice the combined content of
aluminium and silicon.


The wear problems which arise in low speed diesel engines due to cat fines in the fuel oil are
often unexpected and occur even when the fuel analysis indicates that the fuel oil quality is
good. When the fuel oil fulfils the specification of maximum 80 mg/Kg aluminium and silicon,
there can still be problems with cat fines for the following reasons:
       • More cat fines are present in the fuel than appear in the analysis results.
       • Cat fines have accumulated in the sediment of the fuel tank from previous bunkers and
         are mixed into the fuel when the sediment is churned up in bad weather.
       • Cat fines are not sufficiently removed in the separator before the fuel is used.
The fuel at engine inlet must contain maximum 15 mg/Kg aluminium and silicon, but it is not
always helpful to analyse the fuel at engine inlet, when by the time the results have been
received the fuel has already been used and it is not possible to be certain that the analysis
results are fully representative for the rest of the bunker.
With replicas taken by our service engineers from the liner surface we are able to determine if
excessive wear is either caused by abrasive particles e.g. cat fines, cold corrosion or by a fault in
the material and machining of the cylinder liner.
There is less risk of cat fines causing damage to the engine if fuel oil with maximum 30 mg/Kg
combined aluminium and silicon content is bunkered. This limit is fulfilled by the great majority
of commercially available fuel oils.


We have so far published the following G + S Service Bulletins which are valid for SULZER Diesel Engines:
5-1           dated 01.10.71     Treatment of Cooling Water for Diesel Engines
2S-1          dated 15.08.74     Recommendations for Propeller Design, Interrelationship between
                                 Engine / Propeller
4S-1          dated   18.11.94   Detachable Handwheel for Indicator Valve on 4-Stroke Engines
G-3.1         dated   06.10.93   Diesel Engine Fuels
G-5.1         dated   31.08.98   Heading of Service Bulletins their Designation, Purpose and Distribution
G-6.2         dated   23.08.99   Training Courses for Customers / Maintenance Videos
G-7           dated   29.08.97   Return of Components to Wärtsilä NSD Switzerland Ltd
G-8           dated   25.01.99   Year 2000 Compliance
G-9           dated   06.10.99   Catalyst Fines in Heavy Fuel Oil

Should you not be in possession of the above mentioned documentation suitable for your plant, kindly contact
your local Wärtsilä NSD representative for your copy.

                                                   6/8                            Service Bulletin G-9
            Vent chamber in funnel
                                                                             As example drawn
                                                                              for RTA engines

                                                                                                From HFO transfer pump

                                                                                           From engine / feed system

                                                                                                 From auxiliary engines

                      01                        02               03                              15

                                                                                            To sludge or overflow tank

                                                                                                           To feed pump
                                                                                                To daily water drain tank
                                                                                                           To feed pump
                      To HFO transfer pump                                                           To auxiliary engines
                                                                                                 From MDO storage tank
                                                                                                  To MDO transfer pump
                                                                                                    To MDO storage tank

           05                 07                    10           10

           04                                            08           09

                                                                                                  From lub. oil separator
                                                                                                     From sludge pump
                               From drain pipes                                                         To sludge pump
                           From auxiliary engines
                               To transfer pump

                12                                                                               11

HFO pipes, heated and insulated            01   HFO settling tank               09 Self cleaning HFO / MDO
MDO pipes, uninsulated                     02   HFO daily tank                     separator
Fuel oil pipes, heated and insulated       03   MDO daily tank                  10 Three way valve
MDO pipes, uninsulated                     04   Suction filter                  11 Sludge tank
Drain / overflow pipes, insulated          05   HFO separator supply pump       12 Fuel oil overflow tank
Air vent pipes                             06   HFO / MDO separator supply pump 13 Air vent collector
Drain pipes                                07   HFO pre heater                  14 Air vent manifold
                                           08   Self cleaning HFO separator     15 OPTIONAL Secondary
                                                                                   Automatic filtering unit
                     Fig. 3          Fuel Oil Tanks and Treatment
                                     Arrangement with Filtering Unit

                                                         7/8                     Service Bulletin G-9
                          Fuel Oil Feed Pump
                Fuel Oil Suction Filter, heated
 Three Way Valve, manual or remote controlled
                     From MDO Daily Tank                                                                                         OPTIONAL Secondary
                                                                                                                                 Automatic Filter (Item 15)
                     From HFO Daily Tank                                                                                         Mesh Size 0.01mm

                                                            Pressure Regulating Valve
                                                                                                                                               Flow Meter
            To Sludge or Overflow Tank
            To HFO Daily Tank
                       From Steam Supply

                                               1                                          Main Engine
                                               2                                          Pressure Retaining Valve
                                               7                                          Fuel Oil Filter

                                           6       4

                                           5       3
      To Condensate Manifold


                                                                                                Fuel Oil Booster Pump                 Mixing Unit, heated
                                                                                                                                      and insulated

To Overflow Tank

To Oily Water Drain Tank                                                                                                                As example drawn
                                                                                                                                         for RTA engines
                                                       HFO pipes, heated and insulated                        Heating piping
                                                       MDO pipes, uninsulated                                 Air vent pipes
                                                       Fuel oil drain pipes, insulated                        Drain pipes
                                                       Pipes on engine / pipe connections                     Pressure indicator
               1                                       Fuel oil inlet                                         Differential pressure, Alarm High
                                                                                                              Differential pressure indicator
               2                                       Fuel oil outlet                                        Viscosity, Alarm High
               3                                       Leakage from fuel pump and                       *1)   The return pipe may also be led
                                                       pressure piping casing                                 to the HFO daily tank
               4                                       Heating piping to fuel                           *2)   Existence depending on engine
                                                       circulation, inlet *2)                                 type
                 5                                     Heating piping to fuel circulation, outlet *2)
                 6                                     Heating piping for fuel, inlet
                 7                                     Heating piping for fuel, outlet

                                                                  Fig. 4        Fuel Oil System with Automatic Filter

                                                                                               8/8                         Service Bulletin G-9

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